Chaplin is often referred to as the most important artist produced by the cinema. He was once dubbed the funniest man alive, and the most popular and best-known human being in the world. Yet, some time before his death in 1977, it was fashionable to prefer Buster Keaton, both as a performer and director of his own work.

The usual reasons given were that Chaplin was regarded either as a chronic sentimentalist or, conversely, as an icon who damaged his popular reputation by having ideas beyond his station. There is one Chaplin film, however, which more than equalled any of Keaton's: Monsieur Verdoux, which was made in 1947, and perversely attacked at the time for being utterly unsentimental.

It was certainly provocative. Chaplin played Verdoux, a character inspired by Landru, the real-life seducer and murderer of rich women who operated during the first world war, when eligible men were scarce, and was executed soon afterwards.

The real man, though charming, was clearly evil. But Chaplin, moving him forward in time to the 30s, makes him a victim of the Great Depression - a redundant bank clerk attempting to find any means at his disposal to protect his crippled wife and family by bigamously courting and marrying rich women, securing their property and then returning home with the booty.

You could say that, in breaking the taboos of that (or any) society, Verdoux was actually illustrating its hypocrisy: at the time the film was made the millions of war casualties were being thought of as more a consequence of the fight for civilisation than as a painful illustration of the foolishness of power politics.

Perhaps the philosophy behind Monsieur Verdoux, Chaplin's most pessimistic and gag-free film, was simplistic. But his sarcastic and ironic gravity was astonishing for the time.

Eventually, Verdoux, doubling up as Varney, Bonheur and Floray, is caught and loses everything, including his wife and son. But then he becomes the accuser - a murderer taught to kill by the society that spawned him. "Wars, conflict," he says in prison before his execution, "it's all business. One murder makes a villain; millions a hero. Numbers sanctify."

The film, in which Chaplin used sound as effectively as he ever did by dint of a clever if talky screenplay, is not without humour: such as the famous sequence when Verdoux, intent on another murder, falls into the water and is saved by his victim (the gloriously obstreperous Martha Raye, who has already somehow avoided the poison he has made for her).

Verdoux is nothing like the Little Tramp whom the world loved. He is a dapper, elderly man sporting a little French moustache, at one point carefully cutting roses in the garden as an incinerator burns the remains of his latest victim. The only point at which the tramp comes to mind is when Verdoux walks calmly towards his execution.

Chaplin hoped his central character would somehow express the pessimistic times in which he lived: "he is frustrated, bitter and, at the end, pessimistic. But he is never morbid."

The European public agreed, especially in France where half a million people saw the film - a huge number in those days. But in America, with the McCarthy witchhunts beginning, Monsieur Verdoux was ludicrously considered 'communistic' and flopped badly.

Even now, it is not generally considered one of Chaplin's best films. But though not characteristic, it leaves an indelible memory. Few remember, incidentally, that its story was taken not only from history, but from an idea by Orson Welles - who might well have thought about playing Verdoux himself.